I'm trying to find one simple number:
* The average mass of food consumed daily by an average adult human.
I can find lots of statistics on caloric intake, but calories are the energy derived from food and certainly not equivalent to the amount of mass taken in. Knowing the exact amount of mass is important because we need to know how much fresh food we need to carry into space. We can't dehydrate food because this is the modern universe where everyone lives in space and dehydrated food is just disgusting. So...
I can make some extrapolations, but sadly they're inconclusive.
From the amount of food that humans intake by looking at statistics from The Canadian Encyclopedia (not attributed to a specific research paper), which say that a human passes 500 mL of urine and 115 grams of feces per day. Assuming that the person is healthy, they would look at around 1 litre of water per day from liquid consumption, getting the rest of their water from the fresh food they take in. (Not necessarily fresh water. Coffee, tea, and other drinks provide plenty of water too. The idea that coffee, tea, and other such caffeinated beverages provide negative fluid intake is a myth.)
Assuming that those 115 grams of feces are one-quarter dietary fibre and undigestible material, and three-quarters waste bacteria (fecal matter is mostly made up of dead microbiota, if you weren't aware... cool, huh?), that's looking at about 30 grams of fibre per day, and going by the average diet which recommends 25 to 40 grams of fibre per day, that's about dead right. (In this case, I'm assuming that the fecal matter has been completely dehydrated.)
Except that still doesn't tell us how much food we take in per day.
I can find only one source from a moderately-biased source that indicates 1500-1775 pounds per year as the trend from 1970 to 2000.
Now we'll do some more assumptions:
First, let's assume that human beings these days are eating too much food. So, let's find the average between 1970 and 2000, since we'll assume that we need to consume a larger amount of food than in 1970, since humans are getting more massive in general.
( 1500 + 1775 ) / 2 = 1637.5
Let's round that to a nice even 1640, just for simplicity. Since I don't like Imperial units, though, let's convert that to kilograms.
1640 pounds in kilograms = 743.891487
So, 745 kg per year is close enough. We're gaining more and more error due to rounding as we go, but this is just a baseline. Let's divide that by 365 days per year to find daily consumption mass.
745 / 365 = 2.04109589
Isn't that a convenient number? Almost 2 kilograms exactly!
So there you have it. How much food does the average person eat in one day? 2 kilograms, or roughly 4 pounds and 7 ounces.
Sadly, this is dependent on just one source, so I'll keep my eyes on the sky to see if any little birds have other answers.